Composite laminate structures offer a variety of properties not available in metal counterparts, and are extensively utilized in aerospace, automotive, marine and other applications. Most standard composite laminate fabrication techniques result in a composite laminate structure of individual layers or piles consisting of fiber reinforcement in a resin matrix, the matrix resin being relatively weak without the reinforcement. Interlaminar properties of such a composite laminate structure are weak in comparison with in-plane properties of the composite. For example, the weak interply region is an area for each crack propagation. Cracks can be caused by thermal effects, impact events or the presence of holes or edges. Structural failure can often be traced to interply cracking. Impact damaged panels will often fail catastrophically, when subject to compression or flexural loading. Also, the presence of such cracks severely reduces the compressive strength of the composite laminate and can lead to early delamination and failure.
A number of methods for improving the strength of such composite laminate structures have been investigated and include the use of stitching, stapling and needling. Such techniques tend to damage the main reinforcement fibers in the composite laminate and cause a reduction of in-plane properties. Also, the uncured composite laminate lay-ups must be removed from the lay-up tool and passed through the stitching or needling machine. This operation can cause further damage, particularly if the laminate is larger or of complicated shape.
It is an object of this invention to provide an improved method of composite laminate reinforcement which obtains the benefit of stitching, in terms of limiting delamination, while at the same time minimizing damage to the uncured laminate and its main reinforcement structures.
It is a further object of this invention to incorporate such a method in an apparatus which is portable, fast acting and applicable to curved surfaces, can be readily utilized over a layup on-tool to quickly reinforce critical areas (leading edges, around holes, fasteners, along stringers, etc.) and can also be utilized without removal of the layup from its mold thus avoiding handling problems associated with the stitching and stapling processes.